BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to fuel control devices for fuel injection unit pumps or injectors. More particularly, this invention relates to devices and methods for adjusting the quantity of fuel delivered by fuel injectors under different engine operating conditions.
2. Description of the Related Art
The control of fuel delivery over a complete spectrum of engine operating conditions is a critical consideration in controlling emissions as well as ensuring efficient and reliable engine operation. During start up a rich air/fuel mixture may be required to aid ignition. After starting, it is desirable to adjust fuel delivery in accordance with demand such that increased fuel is delivered when the engine is operating under load and fuel delivery is limited when the engine is operating under stable state conditions. A number of mechanisms and techniques have been advanced for implementing the desired fuel supply characteristics in a fuel injected internal combustion engine.
For example, it is known to equip fuel injection unit pumps with a control arm for rotating a pumping plunger in its bore to change the alignment of channels on the plunger relative to fill/spill ports defined by the bore, thereby adjusting the injection duration and thus the quantity of the fuel injected. A control rack connects to each of the unit pump control arms such that movement of the control rack simultaneously adjusts fuel delivery from multiple unit pumps.
It is also known to use a throttle position sensor to determine engine loading conditions and the need for increased fuel delivery. The throttle position sensor produces an electronic signal input to a fuel injection control module, which in turn electrically controls the position of the control rack to adjust fuel delivery commensurate with engine operating conditions. While this type of fuel control has proven suitable for its intended purpose, there are concerns about the reliability and cost associated with such electronic systems.
An object of the present invention is to provide a new and improved control for a fuel injection pump which may take the form of a unit pump/injector.
Another object of the invention is to provide a new and improved control for enhancing fuel supply during engine starting and adjustably limiting fuel supply during later engine operation in accordance with engine operating conditions.
A further object of the invention is to provide a new and improved fuel supply control having improved reliability and efficient and durable construction.
These and other objects of the present invention are achieved by a control mechanism that functions as a dual stage controller that is alternately and independently responsive to engine oil pressure and intake manifold pressure. The control adjusts the supply of fuel by operating on a rack rod connected to a control rack which is in turn arranged to control fuel delivery by one or more unit pumps. The rack rod is fixed to a reciprocable control piston mounted in a base. Engine oil pressure is delivered as a control input to one end of the piston bore. Manifold air pressure acts on a diaphragm to deliver another control input which acts on the control piston through a control rod attached to the diaphragm. The diaphragm and associated control rod are axially opposed to the end of the bore to which engine oil pressure is delivered.
During engine start up, oil pressure is low and a spring bias moves the control piston (and the connected rack rod and control rack) in a direction to increase fuel delivery. After start up, increasing oil pressure resists the spring bias to move the control piston to reduce fuel delivery. A regulator is arranged to limit the maximum oil pressure delivered to the control piston such that, after start up, the position of the control piston is not affected by normal fluctuations in engine oil pressure. During start up, the control piston position is dependent upon engine oil pressure independent of manifold air pressure. During normal engine operation, e.g., after start up, the position of the control piston is dependent upon intake manifold air pressure, with increasing manifold air pressure moving the control piston in a direction to deliver more fuel. Generally speaking, increased intake manifold air pressure indicates increased loading on the engine and an advanced throttle position and the need for increased fuel delivery. After start up, the control piston position is no longer dependent upon engine oil pressure (because of the regulator described above) so that the two control inputs, engine oil pressure and intake manifold air pressure act substantially independently to control fuel delivery.